How Drainage Water and Sub-Irrigation Impact Water Quality

Chad Davison

The soils in the Red River Valley (RRV) are generally fine textured and drain very slowly. At the same time, the RRV also receives the lowest amount of annual rainfall compared to the rest of the state. That rainfall is not distributed evenly throughout the year, with excessive moisture commonly present during spring and less precipitation later during the growing season.

The focus of this project is to monitor water quality, water table level, and yield in the proposed subirrigated corn field. The field will be split into three different zones. Each zone will be managed differently in respect to controlled drainage and sub-irrigation management. Soil moisture sensors placed in the field, along with rain gauges will help determine the need for sub-irrigation. Zone one will be managed as a conventional tile system that is open all year and sub-irrigation will not be used. The water table on zones two and three will be managed at different heights throughout the growing season by changing the heights of the stop logs in the control structures. Irrigation water will be pumped back into the tile of zones two and three to provide water for the corn crop based on weather data, rain gauge data, and soil moisture sensors.

By managing the water table differently in each zone, we will be able to make informed management decisions that maximize yield while maintaining a focus on improved water quality coming from the tile outlets. Throughout the growing season, water grab samples will be taken from the tile outlet of each of the three zones. The water samples will be sent to a lab to be tested for nitrate-nitrogen. Combining water flow and nitrate-nitrogen concentration data will enable the estimation of nitrate-nitrogen load loss on a per acre basis